Process for producing fuel cell electrode

ABSTRACT

Disclosed are processes for producing a fuel cell electrode and a membrane electrode assembly. In one preferred embodiment, the process comprises (a) preparing a suspension of catalyst particles dispersed in a liquid medium containing a polymer dissolved or dispersed therein; (b) dispensing the suspension onto a primary surface of a substrate selected from an electronically conductive catalyst-backing layer (gas diffuser plate) or a solid electrolyte membrane; and (c) removing the liquid medium to form the electrode that is connected to or integral with the substrate, wherein the polymer is both ion-conductive and electron-conductive with an electronic conductivity no less than 10 −4  S/cm and ionic conductivity no less than 10 −5  S/cm and the polymer forms a coating in physical contact with the catalyst particles or coated on the catalyst particles.

FIELD OF THE INVENTION

This invention relates to a process for producing a fuel cell electrode,catalyst-coated membrane (CCM), and membrane-electrode assembly (MEA).The electrode featuring ion- and electro-conductive electro-catalystcomposition, the CCM, and the MEA are particularly useful for protonexchange membrane-type fuel cells.

BACKGROUND OF THE INVENTION

The proton exchange membrane or polymer electrolyte membrane fuel cell(PEM-FC) has been a topic of highly active R&D efforts during the pasttwo decades. The operation of a fuel cell normally requires the presenceof an electrolyte and two electrodes, each comprising a certain amountof catalysts, hereinafter referred to as electro-catalysts. Ahydrogen-oxygen PEM-FC uses hydrogen or hydrogen-rich reformed gases asthe fuel while a direct-methanol fuel cell (DMFC) uses methanol solutionas the fuel. The PEM-FC and DMFC, or other direct organic fuel cells,are collectively referred to as the PEM-type fuel cell.

A PEM-type fuel cell is typically composed of a seven-layered structure,including a central polymer electrolyte membrane for proton transport,two electro-catalyst layers on the two opposite sides of the electrolytemembrane in which chemical reactions occur, two gas diffusion layers(GDLs) or electrode-backing layers stacked on the correspondingelectro-catalyst layers, and two flow field plates stacked on the GDLs.Each GDL normally comprises a sheet of porous carbon paper or cloththrough which reactants and reaction products diffuse in and out of thecell. The flow field plates, also commonly referred to as bipolarplates, are typically made of carbon, metal, or composite graphite fiberplates. The bipolar plates also serve as current collectors. Gas-guidingchannels are defined on a surface of a GDL facing a flow field plate, oron a flow field plate surface facing a GDL. Reactants and reactionproducts (e.g., water) are guided to flow into or out of the cellthrough the flow field plates. The configuration mentioned above forms abasic fuel cell unit. Conventionally, a fuel cell stack comprises anumber of basic fuel cell units that are electrically connected inseries to provide a desired output voltage. If desired, cooling andhumidifying means may be added to assist in the operation of a fuel cellstack.

Several of the above-described seven layers may be integrated into acompact assembly, e.g., the membrane-electrode assembly (MEA). The MEAtypically includes a selectively permeable polymer electrolyte membranebonded between two electrodes (an anode and a cathode). A commonly usedPEM is poly(perfluoro sulfonic acid) (e.g., Nafion® from du Pont Co.),its derivative, copolymer, or mixture. Each electrode typicallycomprises a catalyst backing layer (e.g., carbon paper) and anelectro-catalyst layer disposed between a PEM layer and the catalystbacking layer. Hence, in actuality, an MEA may be composed of fivelayers: two catalyst backing, two electro-catalyst layers, and one PEMlayer interposed between the two electro-catalyst layers. Mosttypically, the two electro-catalyst layers are coated onto the twoopposing surfaces of a PEM layer to form a catalyst-coated membrane(CCM). The CCM is then pressed between a carbon paper layer (the anodebacking layer) and another carbon paper layer (the cathode backinglayer) to form an MEA. It may be noted that, some workers in the fieldof fuel cells refer a CCM as an MEA. Commonly used electro-catalystsinclude noble metals (e.g., Pt), rare-earth metals (e.g., Ru), and theiralloys. Known processes for fabricating high performance MEAs involvepainting, spraying, screen-printing and hot-bonding catalyst layers ontothe electrolyte membrane and/or the catalyst backing layers.

An electro-catalyst is needed to induce the desired electrochemicalreactions at the electrodes or, more precisely, at theelectrode-electrolyte interfaces. The electro-catalyst may be a metalblack, an alloy or a supported metal catalyst, for example, platinumsupported on carbon. In real practice, an electro-catalyst can beincorporated at the electrode-electrolyte interfaces in PEM fuel cellsby applying it in a layer on either an electrode substrate (e.g., asurface of a carbon paper-based backing layer) or a surface of themembrane electrolyte. In the former case, electro-catalyst particles aretypically mixed with a liquid to form a slurry or ink, which is thenapplied to the electrode substrate. While the slurry preferably wets thesubstrate surface to some extent, it must not penetrate too deeply intothe substrate, otherwise some of the catalyst will not be located at thedesired membrane-electrode interface. In the latter case,electro-catalyst particles are coated onto the two primary surfaces of amembrane to form a catalyst-coated membrane (CCM).

Electro-catalyst sites must be accessible to the reactants (e.g.,hydrogen on the anode side and oxygen on the cathode side), electricallyconnected to the current collectors, and ionically connected to theelectrolyte membrane layer. Specifically, electrons and protons aretypically generated at the anode electro-catalyst. The electronsgenerated must find a path (e.g., the backing layer and a currentcollector) through which they can be transported to an external electriccircuit. The protons generated at the anode electro-catalyst must bequickly transferred to the electrolyte (PEM) through which they migrateto the cathode. Electro-catalyst sites are not productively utilized ifthe protons do not have a means for being quickly transported to theion-conducting electrolyte. For this reason, coating the exteriorsurfaces of the electro-catalyst particles and/or electrode backinglayer (carbon paper or fabric) with a thin layer of an ion-conductiveionomer has been used to increase the utilization of electro-catalystexterior surface area and increase fuel cell performance by providingimproved ion-conducting paths between the electro-catalyst surface sitesand the electrolyte membrane. Such an ion-conductive ionomer istypically the same material used as the PEM in the fuel cell. An ionomeris an ion-conducting polymer, which can be of low, medium or highmolecular weight. For the case of a PEM fuel cell, the conducting ion isthe proton and the ionomer is a proton-conducting polymer. The ionomercan be incorporated in the catalyst ink or can be applied on thecatalyst-coated substrate afterwards. This approach has been followed byseveral groups of researchers, as summarized in the following patents:

-   1) D. P. Wilkinson, et al., “Impregnation of micro-porous    electro-catalyst particles for improving performance in an    electrochemical fuel cell,” U.S. Pat. No. 6,074,773 (Jun. 13, 2000).-   2) J. Zhang, et al., “Ionomer impregnation of electrode substrate    for improved fuel cell performance,” U.S. Pat. No. 6,187,467 (Feb.    13, 2001).-   3) I. D. Raistrick, “Electrode assembly for use in a solid polymer    electrolyte fuel cell,” U.S. Pat. No. 4,876,115 (Oct. 24, 1989).-   4) M. S. Wilson, “Membrane catalyst layer for fuel cells,” U.S. Pat.    No. 5,211,984 (May 18, 1993).-   5) J. M. Serpico, et al., “Gas diffusion electrode,” U.S. Pat. No.    5,677,074 (Oct. 14, 1997).-   6) M. Watanabe, et al., “Gas diffusion electrode for electrochemical    cell and process of preparing same,” U.S. Pat. No. 5,846,670 (Dec.    8, 1998).-   7) T. Kawahara, “Electrode for fuel cell and method of manufacturing    electrode for fuel cell,” U.S. Pat. No. 6,015,635 (Jan. 18, 2000).-   8) S. Hitomi, “Solid polymer electrolyte-catalyst composite    electrode, electrode for fuel cell, and process for producing these    electrodes,” U.S. Pat. No. 6,344,291 (Feb. 5, 2002).-   9) S. Hitomi, et al. “Composite catalyst for solid polymer    electrolyte-type fuel cell and process for producing the same,” U.S.    Pat. No. 6,492,295 (Dec. 10, 2002).

However, this prior-art approach of ionomer impregnation into theelectrode layer and/or onto electro-catalyst particle surfaces has aserious drawback in that the ionomer, although ion-conducting(proton-conducting), is not electronically conducting. This is due tothe consideration that a proton-exchange membrane, when serving as thesolid electrolyte layer, cannot be an electronic conductor; otherwise,there would be internal short-circuiting, resulting in fuel cell failureand possible fire hazard. Such an electronically non-conductivematerial, when coated onto the surface of a catalyst particle or carbonpaper fiber, will render the catalyst particle or carbon fiber surfaceelectronically non-conductive. This would prevent the electronsgenerated at the catalyst sites from being quickly collected by theanode electrode substrate layer and the current collector, therebysignificantly increasing the Ohmic resistance and reducing the fuel cellperformance.

A measure of the fuel cell performance is the voltage output from thecell for a given current density. Higher performance is associated witha higher voltage output for a given current density or higher currentdensity for a given voltage output. More effective utilization of theelectro-catalyst, particularly through optimizing the electron and iontransfer rates, enables the same amount of electro-catalyst to induce ahigher rate of electrochemical conversion in a fuel cell resulting inimproved performance. This was the main object of the present invention.

SUMMARY OF THE INVENTION

The present invention provides a process for producing a fuel cellelectrode featuring an electro-catalyst composition that comprises (a) acatalyst un-supported or supported on an electronically conducting solidcarrier; and (b) an ion-conductive and electron-conductive coatingmaterial in physical contact with the catalyst, coated on the catalyst,and/or coated on a surface of the carrier, wherein the coating materialhas an electronic conductivity no less than 10⁻⁴ S/cm and ionconductivity no less than 10⁻⁵ S/cm. Preferably, the electronicconductivity is no less than 10⁻² S/cm and the ion proton conductivityis no less than 10⁻³ S/cm. The catalyst may be selected from transitionmetals, alloys, mixtures, and oxides that can be made into nano-scaledparticles that stand alone or are supported on a conducting materialsuch as carbon black.

In one preferred embodiment, the presently invented process comprises(a) preparing a suspension of catalyst particles dispersed in a liquidmedium containing a polymer dissolved or dispersed therein; (b)dispensing the suspension onto a primary surface of a substrate selectedfrom an electronically conductive catalyst-backing layer (gas diffuserplate) or a solid electrolyte membrane; and (c) removing the liquidmedium to form the electrode that is connected to or integral with thesubstrate, wherein the polymer is both ion-conductive andelectron-conductive. This polymer substantially constitutes the coatingmaterial that helps to establish two intertwine networks of chargetransport paths, one for electrons and the other for ions (which areprotons or hydroxide ions in a PEM-type fuel cell).

In the case of a solid electrolyte membrane (PEM layer) serving as thesubstrate, this process acts to deposit a desirable catalyst compositionto form a layer of catalytic electrode onto a first primary surface ofthe PEM layer. The process may further comprise a step of depositinganother layer of catalytic electrode to a second primary surface of thePEM layer (typically opposite to the first primary surface) to form acatalyst-coated membrane (CCM). The process further includes the step ofsandwiching the CCM between two gas diffuser layers (GDLs) to form amembrane-electrode assembly (MEA). This process can be a continuous,roll-to-roll process for the mass production of MEAs at a low cost.

In the case of a gas diffuser layer (a first GDL) serving as thesubstrate, this process (steps (a)-(c)) acts to deposit a catalyticelectrode onto a primary surface of the first GDL which supports thiselectrode layer. The process may further comprise a step of depositing acatalytic electrode to a primary surface of a second GDL and anotherstep of sandwiching a PEM layer between the electrode layer of the firstGDL and the electrode layer of the second GDL to form an MEA. Again,this process can be a continuous, roll-to-roll process for the massproduction of MEAs at a low cost.

Preferably, the coating material comprises a polymer which is an ion-and electron-conductive polymer or a mixture of a proton-conductingpolymer and an electron-conducting polymer.

The proton-conducting polymer may be selected from the group consistingof poly(perfluoro sulfonic acid), sulfonated polytetrafluoroethylene,sulfonated perfluoroalkoxy derivatives of polytetrafluoroethylene,sulfonated polysulfone, sulfonated poly(ether ketone), sulfonatedpoly(ether ether ketone), sulfonated polystyrene, sulfonated polyimide,sulfonated styrene-butadiene copolymers, sulfonated polychloro-trifluoroethylene (PCTFE), sulfonated perfluoroethylene-propylenecopolymer (FEP), sulfonated ethylene-chlorotrifluoroethylene copolymer(ECTFE), sulfonated polyvinylidenefluoride (PVDF), sulfonated copolymersof polyvinylidenefluoride with hexafluoropropene andtetrafluoroethylene, sulfonated copolymers of ethylene andtetrafluoroethylene (ETFE), polybenzimidazole (PBI), their chemicalderivatives, copolymers, blends and combinations thereof.

The electrically conducting polymer may comprise a polymer selected fromthe group consisting of sulfonated polyaniline, sulfonated polypyrrole,sulfonated poly thiophene, sulfonated bi-cyclic polymers, theirderivatives, and combinations thereof. These polymers are themselvesalso good proton-conductive materials.

Another preferred embodiment of the present invention is a process ofproducing a fuel cell electrode on a substrate selected from a gasdiffuser layer (e.g., carbon paper or cloth) or a solid electrolytemembrane. The process comprises (a) preparing a first suspension orsolution of a first liquid medium containing a first ion- andelectron-conductive polymer dissolved or dispersed therein (butcontaining no catalyst); (b) dispensing this first suspension orsolution onto the substrate and removing the first liquid to form alayer of first conductive polymer adhered to the substrate; and (c)depositing a catalyst composition onto the first conductive polymer withthe catalyst composition being bonded to, mixed with or integral withthe first conductive polymer to form the electrode. This electrode ischaracterized in that it comprises catalyst particles coated with or inphysical contact with a conductive phase comprising the first conductivepolymer and that this conductive phase has an electronic conductivity noless than 10⁻⁴ S/cm and ionic conductivity no less than 10⁻⁵ S/cm. Thisstep of depositing a catalyst composition may comprise (i) dispensing asecond suspension of a second liquid medium with catalyst particlesdispersed therein and a second ion- and electron-conductive polymerdissolved or dispersed therein and (ii) removing the second liquid toform the catalyst composition wherein the second conductive polymer hasan electronic conductivity no less than 10⁻⁴ S/cm and ionic conductivityno less than 10⁻⁵ S/cm. This second conductive polymer may be the samematerial as the first conductive polymer. Alternatively, this secondconductive polymer may be mixed with the first conductive polymer duringthe deposition step to form the cited conductive phase.

Alternatively, this step of depositing a catalyst composition maycomprise (i) dispensing a second suspension of a second liquid mediumwith a molecular metal precursor dispersed or dissolved therein and asecond ion- and electron-conductive polymer dissolved or dispersedtherein and (ii) converting the precursor to catalyst particles andremoving the second liquid to form the catalyst composition wherein thesecond conductive polymer has an electronic conductivity no less than10⁻⁴ S/cm and ionic conductivity no less than 10⁻⁵ S/cm. This secondconductive polymer may be the same material as the first conductivepolymer. Alternatively, this second conductive polymer may be mixed withthe first conductive polymer during the deposition step to form thecited conductive phase.

The incorporation of such an electro-catalyst composition (featuringbi-networks of charge transport paths) in a fuel cell electrode,catalyst-coated membrane, or membrane electrode assembly leads to muchimproved fuel cell performance with much reduced Ohmic loss, highercatalyst utilization efficiency, and higher cell output voltage (giventhe same desired operating current density).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Schematic of a prior-art PEM fuel cell electrode structure.

FIG. 2 Schematic of another prior-art PEM fuel cell electrode structure.

FIG. 3 A three-material model for a local catalyst-electrolyte-carbonfiber region in a prior-art fuel cell electrode.

FIG. 4 Schematic of an electrode structure according to a preferredembodiment of the present invention.

FIG. 5 The electron and proton conductivities of an ion-conductive andelectron-conductive polymer mixture.

FIG. 6 The polarization curves of two fuel cells, one containingelectrode catalyst particles coated with an ion- and electron-conductivepolymer blend and the other containing electrode catalyst particlescoated with ion-conductive (but not electron-conductive) polymer(Nafion).

FIG. 7 The polarization curves of two fuel cells, one containingelectrode catalyst particles coated with an ion- and electron-conductivepolymer (sulfonated polyaniline) and the other containing electrodecatalyst particles coated with ion-conductive (but notelectron-conductive) polymer (Nafion).

FIG. 8 (a) Schematic of a preferred embodiment of the invented processfor producing a membrane-electrode assembly on a continuous basis; (b)Another preferred embodiment of the invented process for producing amembrane-electrode assembly on a continuous basis; and (c) A preferredembodiment of the invented process for producing a catalyst-coatedmembrane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A hydrogen-oxygen PEM-FC using hydrogen gas as the fuel and oxygen asthe oxidant may be represented by the following electrochemicalreactions:Anode:H₂→2H⁺+2e⁻  (Eq.(1))Cathode:½O₂+2H⁺+2e⁻→H₂O  (Eq.(2))Total reaction:H₂+½O₂→H₂O  (Eq.(3))

Both electrode reactions proceed only on a three-phase interface whichallows the reception of gas (hydrogen or oxygen) and the delivery orreception of proton (H⁺) and electron (e⁻) at the same time. An exampleof the electrode having such a function is a solid polymerelectrolyte-catalyst composite electrode comprising a solid polymerelectrolyte and catalyst particles. FIG. 1 schematically shows thestructure of such a prior art electrode. This electrode is a porouselectrode comprising catalyst particles 21 and a solid polymerelectrolyte 22 three-dimensionally distributed in admixture and having aplurality of pores 23 formed thereinside. The catalyst particles form anelectron-conductive channel, the solid electrolyte forms aproton-conductive channel, and the pore forms a channel for the supplyand discharge of oxygen, hydrogen or water as product. The threechannels are three-dimensionally distributed and numerous three-phaseinterfaces which allow the reception or delivery of gas, proton (H⁺) andelectron (e⁻) at the same time are formed in the electrode, providingsites for electrode reaction. In this diagram, reference numeral 24represents an ion-exchange membrane (typically the same material as thesolid polymer electrolyte 22) while numeral 25 represents carbon orgraphite fibers in a sheet of carbon paper as a catalyst backing layer.

The preparation of an electrode having such a structure has heretoforebeen accomplished typically by a process that comprises (a) preparing apaste of catalyst particles and, optionally, poly tetrafluoroethylene(PTFE) particles dispersed in a liquid, (b) applying (dispensing,depositing, spraying, or coating) the paste to a surface of a PEM or aporous carbon electrode substrate (carbon paper) of anelectro-conductive porous material to make a catalyst film (normallyhaving a layer thickness of from 3 to 30 μm), (c) heating and drying thefilm, and (d) applying a solid polymer electrolyte solution to thecatalyst film so that the film is impregnated with the electrolyte.Alternatively, the process comprises applying a paste made of catalystparticles, PTFE particles, and a solid polymer electrolyte solution to aPEM or a porous carbon electrode substrate to make a catalyst film andthen heating and drying the film. The solid polymer electrolyte solutionmay be obtained by dissolving the same composition as the aforementionedion-exchange membrane (PEM) in an alcohol. PTFE particles are typicallysupplied with in a solution with the particles dispersed therein. PTFEparticles typically have a particle diameter of approximately 0.2-0.3μm. Catalyst particles are typically Pt or Pt/Ru nano particlessupported on carbon black particles.

The aforementioned solid polymer electrolyte-catalyst compositeelectrode has the following drawbacks: The solid polymerelectrolyte-catalyst composite electrode has a high electricalresistivity, which may be explained as follows. When catalyst particlesare mixed with solid polymer electrolyte solution to prepare a paste,the catalyst particles are covered with solid polymer electrolyte filmhaving extremely low electronic conductivity (10⁻¹⁶-10⁻¹³ S/cm). Uponcompletion of a film-making process to prepare an electrode, pores 32and the non-conductive solid polymer electrolyte 33 tend to separate orisolate catalyst particles 33. The formation of a continuous catalystparticle passage (electron-conducting channel) is inhibited orinterrupted, although a continuous solid electrolyte passage(proton-conducting channel) is maintained, as shown in the sectionalview of electrode of FIG. 2.

Furthermore, by pressing the catalyst-electrolyte composite compositionlayer against the PEM layer to make a catalyst-coated membrane (CCM) ormembrane electrode assembly (MEA), a significant amount of thecarbon-supported catalyst particles tend to be embedded deep into thePEM layer (illustrated by the bottom portion of FIG. 2), making theminaccessible by electrons (if used as a cathode) or incapable ofdelivering electrons to the anode current collector (if used as ananode). As a result, the overall percent utilization of carbon-supportedcatalyst is significantly reduced.

As shown in the upper portion of FIG. 1, the electronicallynon-conducting solid electrolyte 22 also severs the connection betweenthe otherwise highly conductive catalyst-supporting carbon particles 21and the carbon fibers 25 in the electrode-catalyst backing layer (carbonpaper). This problem of solid electrolyte being interposed between acarbon particle and a carbon fiber is very significant and has beenlargely ignored by fuel cell researchers. The degree of severity of thisproblem is best illustrated by considering a three-layer model shown inFIG. 3. The model consists of top, core, and bottom layers that areelectrically connected in series. The top layer represents a carbonfiber material, the bottom layer a carbon black particle material, andthe core layer a solid electrolyte material. The total resistance(R_(S)), equivalent resistivity (ρ_(s)), and conductivity (σ_(s)) of thethree-layer model can be easily estimated. For the top layer (carbonfiber), the properties or parameters are given as follows: conductivity(σ₁), resistivity (ρ₁), resistance (R₁), and thickness (t₁). Similarnotations are given for the other two layers with subscript being “2”and “3”, respectively. FIG. 3 shows that the equivalent conductivity ofthe resulting three-layer model is ρ_(s)=(ρ₁t₁+ρ₂t₂+ρ₃t₃)/(t₁+t₂+t₃).With t₁=10 μm, t₂=1 μm, and t₃=30 nm (0.03 μm), ρ₁=10⁻¹ Ωcm, ρ₂=10⁺¹⁴Ωcm, and ρ₃=10⁺² Ωcm, we have σ_(s)=1/ρs˜10⁻¹³ S/cm. Assume that theelectrolyte layer has a thickness as low as 1 nm (0.001 μm), theequivalent conductivity would be still as low as σ_(s)≈10⁻¹⁰ S/cm. It isclear that the equivalent conductivity of the local electrodeenvironment (three-component model) is dictated by the low conductivityor high resistivity of the solid electrolyte (22 in FIGS. 1 and 33 inFIG. 2). These shockingly low conductivity values (10⁻¹³ to 10⁻¹⁰ S/cm)clearly have been overlooked by all of the fuel cell researchers. Itcould lead to significant power loss (Ohmic resistance) in a fuel cell.

To effectively address the aforementioned issues associated withelectro-catalysts in a fuel cell in general and a PEM-type fuel cell inparticular, we decided to take a novel approach to the formulation ofelectro-catalysts. Rather than using the same solid electrolyte materialas the PEM layer (which is ion-conductive but must be electronicallynon-conductive), we used a solid electrolyte material (that is bothelectron-conductive and ion-conductive) to coat, impregnate, and/orembed catalyst particles, which are un-supported or supported onconductive particles like carbon black. This newly developed ion- andelectron-conductive electrolyte material is also herein after referredto as a coating material. The solid electrolyte layer (e.g., PEM orother ion conductive solids, organic or inorganic) interposed betweenthe anode and the cathode remained to be an ion-conductive (e.g.,proton-conductive), but not electron-conductive. As a result, theelectrons produced at the anode can be quickly collected through the gasdiffuser layer (carbon paper or cloth) and the protons produced at theanode can be quickly transported to and through the solid electrolytemembrane (PEM layer) without producing significant Ohmic losses.Similarly, the electrons that move around the external circuit and comeback to the cathode side can reach the cathode catalyst particleswithout much resistance and the protons that have transported throughthe PEM layer also can easily reach the catalyst particle sites. Withoxygen molecules diffusing through pores or the thin coating materiallayer being present, the cathode chemical reactions can readily proceed.In essence, the presently invented electrode that contains an ion- andelectron-conductive material helps to form two networks of chargetransport paths, one for electrons and the other for protons.

Hence, one of the preferred embodiments of the present invention is aprocess that utilizes a specially formulated electro-catalystcomposition to produce a fuel cell electrode. The composition comprises:(a) a catalyst un-supported or supported on an electronically conductingsolid carrier (e.g., carbon black particles) and (b) an ion-conductingmaterial in physical contact with the catalyst, coated on the catalyst,and/or coated on a surface of the carrier, wherein the ion-conductingmaterial is also electronically conducting with an electronicconductivity no less than 10⁻⁴ S/cm (preferably no less than 10⁻² S/cm)and ion (proton) conductivity no less than 10⁻⁵ S/cm (preferably no lessthan 10⁻³ S/cm). The catalyst may be selected from commonly usedtransition metal-based catalysts such as Pt, Pd, Ru, Mn, Co, Ni, Fe, Cr,and their alloys, mixtures, and oxides (these are given as examples andshould not be construed as limiting the scope of the present invention).Such a composite catalyst (comprising supported or unsupported catalystparticles and the ion- and electron-conductive coating material) can beattached to or coated on a porous carbon paper on one side and attachedto or coated on a PEM layer on another side (FIG. 4). Thision-conductive and electron-conductive material preferably comprises apolymer, which can be a homo-polymer, co-polymer, polymer blend ormixture, a semi-interpenetrating network, or a polymer alloy. In thiscase, one polymer component can be ion-conductive and another oneelectron-conductive. It is also possible that a polymer itself isconductive to both electrons and ions (e.g., protons). Examples will begiven for these cases. The process itself will be described at a latersection.

With this invented catalyst composition, the resulting electrode can beused as either an anode or a cathode. As shown in FIG. 4, when it isused in an anode, hydrogen gas or organic fuel can permeate to theelectrode through the pores 23 or diffuse through the ion- andelectron-conductive electrolyte material 44, which is ultra-thin and canbe readily migrated through via diffusion. Due to its high electronicconductivity, the electrons produced at the catalyst particles 21 can bequickly transported through the electrolyte material 44 to carbon fibers25 of a carbon paper and be collected with little resistance orresistive (Ohmic) loss. The produced protons are also capable ofmigrating through the invented ion- and electron-conductive electrolytematerial 44 (herein after also referred to as the coating orimpregnation material) into the electronically non-conductive PEM layer,which is a conventional solid electrolyte layer interposed between ananode and a cathode.

If used as a cathode catalyst material, this solid electrolyte coatingmaterial 44 allows the electrons that come from the external load to goto the catalyst particle sites where they meet with protons and oxygengas to form water. The protons come from the anode side, through the PEMlayer, and the coating material 44 to reach the catalyst sites. Oxygengas migrates through the pores 23 or the electrolyte coating material 44via diffusion. Again, the electrons are capable of being transportedinto the cathode without any significant Ohmic loss due to the highelectronic conductivity of electrolyte material 44.

In one preferred embodiment, the ion-conductive and electron-conductivecoating material 44 comprises a polymer that is by itself bothion-conductive and electron-conductive. Examples of this type polymerare sulfonated polyaniline compositions, as described by Epstein, et al.(U.S. Pat. No. 5,137,991, Aug. 11, 1992):

where 0≦y≦1, R₁, R₂, R₃, R₄, R₅, and R₆ are independently selected fromthe group consisting of H, SO₃ ⁻, SO₃H, —R₇SO₃ ⁻, —R₇SO₃H, —OCH₃, —CH₃,—C₂H₅, —F, —Cl, —Br, —I, —OH, —O⁻, —SR₇, —OR₇, —COOH, —COOR₇, —COR₇,—CHO, and —CN, wherein R₇ is a C₁-C₈ alkyl, aryl, or aralkyl group, andwherein the fraction of rings containing at least one R₁, R₂, R₃, or R₄group being an SO₃ ⁻, SO₃H, —R₇SO₃ ⁻, or —R₇SO₃H that varies fromapproximately 20% to 100%. It may be noted that this class of polymerswas developed for applications that made use of their electronicproperties. Due to their high electronic conductivity, these polymerscannot be used as a PEM interposed between an anode and a cathode in afuel cell (PEM must be electronically non-conductive to avoid internalshort-circuiting in a fuel cell). Hence, it is no surprise that theproton conductivity of these polymers has not been reported by Epstein,et al.

It is of interest at this juncture to re-visit the issue of ion andelectron conductivities for this coating material. The protonconductivity of a conventional PEM material is typically in the range of10⁻³ S/cm to 10⁻¹ S/cm (resistivity ρ of 10¹ Ω-cm to 10³ Ω-cm). Thethickness (t) of a PEM layer is typically in the vicinity of 100 μm andthe active area is assumed to be A=100 cm². Then, the resistance toproton flow through this layer will be R=ρ(t/A)=10⁻³Ω to 10⁻¹Ω. Furtherassume that the resistance of the catalyst coating material (the ion-and electron-conductive material) will not add more than 10% additionalresistance, then the maximum resistance of the coating layer will be10⁻⁴Ω to 10⁻²Ω. With a coating layer thickness of 1 μm, the resistivityto proton flow cannot exceed 10² Ω-cm to 10⁴ Ω-cm (proton conductivityno less than 10⁻⁴ S/cm to 10⁻² S/cm). With an intended coating layerthickness of 0.1 μm (100 nm), the proton conductivity should be no lessthan 10⁻⁵ S/cm to 10⁻³ S/cm.

Similar arguments may be used to estimate the required electronicconductivity of the coating layer. Consider that the electrons producedat the catalyst surface have to pass through a coating layer (0.1 μm or100 nm thick) and a carbon paper layer (100 μm in thickness with averagetransverse conductivity of 10⁻¹ S/cm to 10⁺¹ S/cm). A reasonablerequirement is for the coating layer to produce a resistance to electronflow that is comparable to 10% of the carbon paper resistance. Thisimplies that the electronic conductivity of the coating material shouldbe in the range of 10⁻³ S/cm to 10⁻¹ S/cm. These values can be increasedor decreased if the coating thickness is increased or decreased. It maybe further noted that conventional PEM materials have an electronicconductivity in the range of 10⁻¹⁶-10⁻¹³ S/cm, which could produce anenormous power loss.

We therefore decided to investigate the feasibility of using sulfonatedpolyaniline (S-PANi) materials as a component of an electro-catalystmaterial. After an extensive study, we have found that the mostdesirable compositions for use in practicing the present invention arefor R₁, R₂, R₃, and R₄ group in Formula I being H, SO₃ ⁻ or SO₃H withthe latter two varied between 30% and 75% (degree of sulfonation between30% and 75%). The proton conductivity of these SO₃ ⁻- or SO₃H-basedS-PANi compositions increases from 3×10⁻³ S/cm to 4×10⁻² S/cm and theirelectron conductivity decreases from 0.5 S/cm to 0.1 S/cm when thedegree of sulfonation is increased from approximately 30% to 75% (with ybeing approximately 0.4-0.6). These ranges of ion and protonconductivities are reasonable, particularly when one realizes that onlya very thin film of S-PANi is used (typically much thinner than 1 μm andcan be as thin as nanometers). A polymer of this nature can be usedalone as an ion- and electron-conductive material. We have further foundthat these polymers are soluble in a wide range of solvents and arechemically compatible (miscible and mixable) with the commonly usedproton-conductive polymers such as those represented by Formula IV-VII,to be described later. Hence, these S-PANi polymers also can be used incombination with an ion- (proton-) conductive polymer to coat theelectro-catalyst particles.

The aforementioned class of S-PANi was prepared by sulfonating selectedpolyaniline compositions after polymer synthesis. A similar class ofsoluble aniline polymer could be prepared by polymerizing sulfonicacid-substituted aniline monomers. The synthesis procedures 26 aresimilar to those suggested by Shimizu, et al. (U.S. Pat. No. 5,589,108,Dec. 31, 1996). The electronic conductivity of this class of materialwas found by Shimizu, et al. to be between 0.05 S/cm and 0.2 S/cm,depending on the chemical composition. However, proton conductivity wasnot measured or reported by Shimizu, et al. We have found that theproton conductivity of this class of polymers typically ranges from4×10⁻³ S/cm to 5×10⁻² S/cm, depending on the degree of sulfonation. Itappears that both ion (proton) and electron conductivities of thesepolymers are well within acceptable ranges to serve as an ion- andelectron-conductive polymer for use in the presently invented fuel cellcatalyst compositions. Again, these polymers are soluble in a wide rangeof solvents and are chemically compatible (miscible and mixable) withcommonly used proton-conductive polymers such as those represented byFormula IV-VII, to be described later. Hence, these polymers not onlycan be used alone as an ion- and electron-conductive polymer, but alsocan be used an electron-conductive polymer component that forms amixture with a proton-conductive polymer.

The needed ion- and electron-conducting coating polymer can be a mixtureor blend of an electrically conductive polymer and an ion-conductivepolymer with their ratio preferably between 20/80 to 80/20. Theelectron-conductive polymer component can be selected from any of the πelectron conjugate chain polymers, doped or un-doped, such asderivatives of polyaniline, polypyrrole, polythiophene, polyacetylen,and polyphenylene provided they are melt- or solution-processable. Aclass of soluble, electron-conductive polymers that can be used in thepresent invention has a bi-cyclic chemical structure represented byFormula II:

wherein R₁ and R₂ independently represent a hydrogen atom, a linear orbranched alkyl or alkoxy group having 1 to 20 carbon atoms, a primary,secondary or tertiary amino group, a trihalomethyl group, a phenyl groupor a substituted phenyl group, X represents S, O, Se, Te or NR₃, R₃represents a hydrogen atom, a linear or branched alkyl group having 1 to6 carbon atoms or a substituted or unsubstituted aryl group, providingthat the chain in the alkyl group of R₁, R₂, or R₃, or in the alkoxygroup of R₁ or R₂ optionally contains a carbonyl, ether or amide bond, Mrepresents H⁺, an alkali metal ion such as Na⁺, Li⁺, or K⁺ or a cationsuch as a quaternary ammonium ion, and m represents a numerical value inthe range between 0.2 and 2. This class of polymers was developed forthe purpose of improving solubility and processability ofelectron-conductive polymers (Saida, et al., U.S. Pat. No. 5,648,453,Jul. 15, 1997). These polymers are also soluble in a wide range ofsolvents (including water) and are chemically compatible (miscible andmixable) with the proton-conductive polymers represented by FormulaIV-VII, to be described later. These polymers exhibit higher electronicconductivity when both R₁ and R₂ are H, typically in the range of 5×10⁻²S/cm to 1.4 S/cm. These polymers are also proton-conductive (protonconductivity of 5×10⁻⁴ S/cm to 1.5×10⁻² S/cm) and hence can be used inthe presently invented catalyst composition, alone or in combinationwith another ion-conductive or electron-conductive polymer.

Polymers which are soluble in water and are electronically conductivemay be prepared from a monomer that has, as a repeat unit, a thiopheneor pyrrole molecule having an alkyl group substituted for the hydrogenatom located in the beta position of the thiophene or pyrrole ring andhaving a surfactant molecule at the end of the alkyl chain (Aldissi, etal., U.S. Pat. No. 4,880,508, Nov. 14, 1989):

In these polymers, the monomer-to-monomer bonds are located between thecarbon atoms which are adjacent to X, the sulfur or nitrogen atoms. Thenumber (m) of carbon atoms in the alkyl group may vary from 1 to 20carbon atoms. The surfactant molecule consists of a sulfonate group(Y=SO₃), or a sulfate group (Y=SO₄), or a carboxylate group (Y=CO₂), andhydrogen (A=H) or an alkali metal (A=Li, Na, K, etc.). Synthesis ofthese polymers may be accomplished using the halogenated heterocyclicring compounds 3-halothiophene or 3-halopyrrole as starting points;these are available from chemical supply houses or may be prepared bymethod known to those skilled in the art. The electronic conductivity ofthese polymers is typically in the range of 10⁻³ S/cm to 50 S/cm.

The ion- or proton-conductive polymer can be any polymer commonly usedas a solid polymer electrolyte in a PEM-type fuel cell. These PEMmaterials are well-known in the art. One particularly useful class ofion-conductive polymers is the ion exchange membrane material havingsulfonic acid groups. These materials are hydrated when impregnated withwater, with hydrogen ion H⁺ detached from sulfonic ion, SO₃ ⁻. Thegeneral structure of the sulfonic acid membranes that have receivedextensive attention for use in fuel cells and are sold under the tradename Nafion® by E. I. du Pont Company is as follows:

where x and y are integers selected from 1 to 100,000, preferably from 1to 20,000, most preferably from 100 to 10,000. A similar polymer that isalso suitable for use as a PEM is given as:

Sulfonic acid polymers having a shorter chain between the pendantfunctional group (side group) and the main polymer backbone absorb lesswater at a given concentration of functional group in the polymer thando polymers having the general structure as shown by Formula IV and V.The concentration of functional group in the dry polymer is expressed asan equivalent weight. Equivalent weight is defined, and convenientlydetermined by standard acid-base titration, as the formula weight of thepolymer having the functional group in the acid form required toneutralize one equivalent of base. In a more general form, this group ofproton-conducting polymers may be represented by the formula:

where x and y are integers selected from 1 to 100,000, m is an integerselected from 0 to 10 and R is a functional group selected from thegroup consisting of H, F, Cl, Br, I, and CH₃.

Another class of PEM polymer suitable for use as an ion-conductivepolymer in the present invention is characterized by a structure havinga substantially fluorinated backbone which has recurring pendant groupsattached thereto and represented by the general formula:—O(CFR_(f)′)_(b)—(CFR_(f))_(a)—SO₃H  (Formula VII)where a=0-3, b=0-3, a+b=at least 1, R_(f) and R_(f)′ are independentlyselected from the group consisting of a halogen and a substantiallyfluorinated alkyl group having one or more carbon atoms.

The above polymers have a detachable hydrogen ion (proton) that isweakly attached to a counter-ion (e.g., SO₃ ⁻), which is covalentlybonded to a pendant group of the polymer. While the general structuresshown above are representative of several groups of polymers of thepresent invention, they are not intended to limit the scope of thepresent invention. It would become obvious to those skilled in the art,from the relationships presented herein that other sulfonic acidfunctional polymers having pendant chains, sterically hindered sulfonategroups or the like would absorb some water and conduct protons. Forinstance, the derivatives and copolymers of the aforementioned sulfonicacid polymers, alone or in combination with other polymers to formpolymer blends, may also be used as an ion-conductive material in theinvented fuel cell catalyst composition. The aforementioned polymerswere cited as examples to illustrate the preferred mode of practicingthe present invention. They should not be construed as limiting thescope of the present invention.

In summary, the ion- or proton-conducting polymer component of thedesired mixture may be selected from the group consisting ofpoly(perfluoro sulfonic acid), sulfonated poly (tetrafluoroethylene),sulfonated perfluoroalkoxy derivatives of polytetrafluoroethylene,sulfonated polysulfone, sulfonated poly(ether ketone), sulfonatedpoly(ether sulfone ketone), sulfonated poly(ether ether ketone),sulfonated polyimide, sulfonated styrene-butadiene copolymers,sulfonated polystyrene, sulfonated poly chloro-trifluoroethylene(PCTFE), sulfonated perfluoroethylene-propylene copolymer (FEP),sulfonated ethylene-chlorotrifluoroethylene copolymer (ECTFE),sulfonated poly vinylidenefluoride (PVDF), sulfonated copolymers ofpolyvinylidenefluoride with hexafluoropropene and tetrafluoroethylene,sulfonated copolymers of ethylene and tetrafluoroethylene (ETFE),polybenzimidazole (PBI), their chemical derivatives, copolymers, blendsand combinations thereof. These materials have been used as solidelectrolyte materials for various PEM-based fuel cells due to theirrelatively good proton conductivity (typically between 0.1 S/cm and0.001 S/cm).

Any of these ion-conductive materials can be mixed with anelectron-conductive polymer to make a polymer blend or mixture that willbe conductive both electronically and ionically. Such a mixture isprepared preferably by dissolving both the ion-conductive polymer andthe electron-conductive polymer in a common solvent to form a polymersolution. Catalyst particles are then added to this polymer solution toform a suspension, also referred to as a dispersion. Alternatively,catalyst particles may be dispersed in a liquid to obtain a suspension,which is then poured into the polymer solution to form a precursorcomposite catalyst composition. Nano-scaled catalyst particles may beselected from (but not limited to) commonly used transition metal-basedcatalysts such as Pt, Pd, Ru, Mn, Co, Ni, Fe, Cr, and their alloys ormixtures. They are commercially available in a fine powder form or in aliquid with these nano-scaled particles dispersed therein. They may bemanufactured by a powder manufacturing method such as solutionprecipitation, sol-gel conversion, or spray-based powder productionroutes. The suspension containing dispersed catalyst particles(supported or unsupported) and a polymer or polymer mixture (both ion-and electron-conductive) may be coated (via dispensing, spraying,ink-jet printing, screen printing, painting, or brushing, etc.) onto aprimary surface of a gas diffuser plate (electrically conductiveelectrode-backing layer such as a carbon paper or carbon cloth sheet).Upon removal of the liquid medium, the remaining ingredients form anelectrode that is connected to this gas diffuser plate. Alternatively,the suspension may be deposited to one or both primary surfaces of asolid electrolyte membrane to produce a catalyst-coated membrane (CCM).With two diffuser plates sandwiching this CCM we have amembrane-electrode assembly (MEA).

Electro-catalyst particles used in the presently invented process andcomposition can be one of three types or their combinations: (1)unsupported catalyst particles; (2) supported catalysts, such asaggregate particles of carbon black supporting Pt particles; (3)nano-particles. Unsupported catalyst particles are catalyst particlesthat are not supported on the surface of another material. These includesuch materials as platinum black and platinum/ruthenium black which intheir natural form are not necessarily nano-scaled in size. Supportedcatalysts include a catalytically active species dispersed on a supportphase. Thus, one or more highly dispersed active species phases,typically metal or metal oxide clusters or crystallites, with dimensionson the order of about 0.5 nanometers to 10 nanometers that are dispersedover the surface of larger support particles (typically 10 nm to 1 μm).The support particles can be aggregated to form larger aggregateparticles. For example, the support particles can be chosen from a metaloxide. (e.g., RuO₂, In₂O₃, ZnO, IrO₂, SiO₂, Al₂O₃, CeO₂, TiO₂ or SnO₂),aerogels, xerogels, carbon or a combination of the foregoing. Carbonblack particles are popular materials for supporting the dispersedcatalytically active species.

Catalyst nano-particles are particles which have an average size of notgreater than 100 nanometers (preferably smaller than 10 nanometers), andmay be unsupported. The nano-particles most preferably have an averagesize of from about 0.5 to 2 nanometers. Catalyst nano-particles maycomprise metals, metal oxides, metal carbides, metal nitrides or anyother material that exhibits catalytic activity.

Hence, as one preferred embodiment, the presently invented fuel cellelectrode-producing process comprises (a) preparing a suspension ofcatalyst particles dispersed in a liquid medium containing a polymerdissolved or dispersed therein; (b) dispensing the suspension onto aprimary surface of a substrate selected from an electronicallyconductive catalyst-backing layer (gas diffuser plate) or a solidelectrolyte membrane; and (c) removing the liquid medium to form theelectrode that is connected to or integral with the substrate, whereinthe polymer is both ion-conductive and electron-conductive and thepolymer forms a coating in physical contact with the catalyst particlesor coated on the catalyst particles. Again, the presently inventedelectrode that contains an ion- and electron-conductive coating materialhelps to form two networks of charge transport paths, one for electronsand the other for protons.

Alternatively, the electro-catalyst particles may be produced in-situ bydelivering the suspension that contains molecular precursors along withother ingredients to a substrate (e.g., a surface of a carbon paper orPEM layer) and converting the precursors to the catalytically activespecies after deposition via heating, UV curing, or a radiation-inducedreaction. Hence, another preferred embodiment of the present inventionis a process that comprises: (a) preparing a suspension or solutioncomprising a liquid medium, a molecular metal precursor and a polymerdissolved or dispersed in the liquid medium; (b) dispensing thesuspension or solution onto a primary surface of a substrate (anelectronically conductive catalyst-backing layer or a solid electrolytemembrane layer); and (c) converting the molecular metal precursor tocatalyst particles and removing the liquid medium to form the electrodethat is connected to or integral with the substrate, wherein the polymeris both ion-conductive and electron-conductive with an electronicconductivity no less than 10⁻⁴ S/cm and ionic conductivity no less than10⁻⁵ S/cm and the polymer forms a coating in physical contact with thecatalyst particles or coated on the catalyst particles.

A molecular metal precursor is a metal-containing molecular compound,comprising preferably a metal such as platinum, ruthenium, palladium,silver, nickel, cobalt, iron, manganese, or gold. For example, molecularprecursors such as hydrogen hexachloroplatinate, ruthenium chloridehydrate, hydrogen hexachloropallidate, silver nitrate, nickel acetate orpotassium tetra-chloroaurate can be reduced to form nano-scaled catalystparticles. The reducing agent can be any number of alcohols, diols orother reducing compounds such as methanol, ethanol, n-propanol,2-propanol, n-butanol, 2-butanol, ethylene glycol, formaldehyde orN,N-dimethyl formamide. The particles are stabilized from aggregation bythe adsorption of stabilizing polymer molecules on the particlesurfaces. We have found that most of the aforementioned ion- andelectron-conductive polymers or polymer mixtures can be dissolved inalcohol (methanol, ethanol, n-propanol, 2-propanol, n-butanol,2-butanol), mixture of alcohol+water, ethylene glycol, formaldehyde orN,N-dimethyl formamide, which are also good reducing agents. We are alsopleasantly surprised to find that these ion- and electron-conductivepolymers are excellent stabilizing agents. These observations are highlysignificant since the resulting suspension or solution can be verysimple in chemical composition: a liquid medium (e.g., alcohol), an ion-and-electron-conductive polymer (e.g., sulfonated polyaniline), and amolecular metal precursor (e.g., hydrogen hexachloroplatinate). Carbonblack particles can be added to serve as a support for the convertedcatalyst. These particles are well-stabilized by the dissolved polymer.

Preferred metals for the supported electro-catalytically active speciesinclude noble metals, particularly Pt, Ag, Pd, Ru, Os and their alloys.The metal phase can also include a metal selected from the group Ni, Rh,Ir, Co, Cr, Mo, W, V, Nb, Al, Ta, Ti, Zr, Hf, Zn, Fe, Cu, Ga, In, Si,Ge, Sn, Y, La, lanthanide metals and combinations or alloys of thesemetals. Preferred metal alloys include alloys of Pt or Pd with othermetals, such as Ru, Os, Cr, Ni, Mn, Fe, and Co. Particularly preferredamong these is PtRu for use in the DMFC anode and PtCrCo or PtNiCo foruse in the cathode.

Alternatively, metal oxide-carbon electro-catalyst particles thatinclude a metal oxide active species dispersed on a carbon support phasemay be used. The metal oxide can be selected from the oxides of thetransition metals, preferably those existing in oxides of variableoxidation states, and most preferably from those having an oxygendeficiency in their crystalline structure. For example, the metaloxide-based catalytically active species can be an oxide of a metalselected from the group consisting of Au, Ag, Pt, Pd, Ni, Co, Rh, Ru,Fe, Mn, Cr, Mo, Re, W, Ta, Nb, V, Hf, Zr, Ti or Al. A particularlypreferred metal oxide active species is manganese oxide (MnO_(x), wherex is 1 to 2). The supported active species can include a mixture ofdifferent oxides, solid solutions of two or more different metal oxidesor double oxides. The metal oxides can be stoichiometric ornon-stoichiometric and can be mixtures of oxides of one metal havingdifferent oxidation states.

In a particularly preferred embodiment, the molecular metal precursorsare selected from low temperature precursors, such as those that have arelatively low decomposition or conversion temperature. The termmolecular metal precursor refers to a molecular compound that includes ametal atom. Examples include organo-metallics (molecules withcarbon-metal bonds), metal organics (molecules containing organicligands with metal-to-nonmetal bonds) and inorganic compounds such asmetal nitrates, metal halides and other metal salts. The molecular metalprecursor compounds that eliminate ligands by a radical mechanism uponconversion to metal are preferred, especially if the species formed arestable radicals and therefore lower the decomposition temperature ofthat precursor compound. Therefore, preferred precursors to metals usedfor conductors are carboxylates, alkoxides or combinations thereof thatconvert to metals, metal oxides or mixed metal oxides by eliminatingsmall molecules such as carboxylic acid anhydrides, ethers or esters.Metal carboxylates, particularly halogenocarboxylates such asfluorocarboxylates, are particularly preferred metal precursors due totheir high solubility

Particularly preferred molecular metal precursor compounds are metalprecursor compounds containing silver, nickel, platinum, gold,palladium, cobalt, iron, manganese, copper and ruthenium. In onepreferred embodiment of the present invention, the molecular metalprecursor compound comprises platinum. Various molecular precursors canbe used for platinum metal. Preferred molecular precursors for platinuminclude nitrates, carboxylates, beta-diketonates, and compoundscontaining metal-carbon bonds. Divalent platinum (II) complexes areparticularly preferred. Preferred molecular precursors also includeammonium salts of platinates such as ammonium hexachloro platinate(NH₄)₂ PtCl₆, and ammonium tetrachloro platinate (NH₄)₂PtCl₄; sodium andpotassium salts of halogeno, pseudohalogeno or nitrito platinates suchas potassium hexachloro platinate K₂PtCl₆, sodium tetrachloro platinateNa₂PtCl₄, potassium hexabromo platinate K₂PtBr₆, potassium tetranitritoplatinate K₂Pt(NO₂)₂; dihydrogen salts of hydroxo or halogeno platinatessuch as hexachloro platinic acid H₂PtCl₆, hexabromo platinic acidH₂PtBr₂, dihydrogen hexahydroxo platinate H₂Pt(OH)₂; diammine andtetraammine platinum compounds such as diammine platinum chloridePt(NH₃)₂Cl₂, tetraammine platinum chloride [Pt(NH₃)₄]Cl₂, tetraammineplatinum hydroxide [Pt(NH₃)₄](OH)₂, tetraammine platinum nitrite[Pt(NH₂)₄](NO₂)₂, tetrammine platinum nitrate Pt(NH₂)₄(NO₃)₂, tetrammineplatinum bicarbonate [Pt(NH₃)₄](HCO₃)₂, tetraammine platinumtetrachloroplatinate [Pt(NH₃)₄]PtCl₄; platinum diketonates such asplatinum (II) 2,4-pentanedionate Pt(C₅ H₇ O₂)₂; platinum nitrates suchas dihydrogen hexahydroxo platinate H₂ Pt(OH)₂ acidified with nitricacid; other platinum salts such as Pt-sulfite and Pt-oxalate; andplatinum salts comprising other N-donor ligands such as [Pt(CN)₂]⁴⁺.

Platinum precursors useful in organic-based ink suspension compositionsinclude Pt-carboxylates or mixed carboxylates. Examples of carboxylatesinclude Pt-formate, Pt-acetate, Pt-propionate, Pt-benzoate, Pt-stearate,Pt-neodecanoate. Other precursors useful in organic ink compositioninclude aminoorgano platinum compounds including Pt(diaminopropane)(ethylhexanoate). Preferred combinations of platinum precursors andsolvents include: PtCl₄ in H₂O; Pt-nitrate solution from H₂Pt(OH)₆;H₂Pt(OH)₆ in H₂O; H₂PtCl₆ in H₂O; and [Pt(NH₂)₄](NO₃)₂ in H₂O.

Additional examples of molecular metal precursor materials are metalporphyrin complexes which catalyze the reduction of O₂ to OH⁻ but areoxidized during the oxidation of OH⁻. Included in this group are metalporphyrin complexes of Co, Fe, Zn, Ni, Cu, Pd, Pt, Sn, Mo, Mn, Os, Irand Ru. Other metal ligand complexes can be active in these catalyticoxidation and reduction reactions and can be formed by the methodsdescribed herein. Such metal ligands can be selected from the class ofN₄-metal chelates, represented by porphyrins, tetraazaanulens,phtalocyanines and other chelating agents. In some cases the organicligands are active in catalyzing reduction and oxidation reactions. Insome cases the ligands are active when they remain intact, as might bethe case for an intact porphyrin ring system, or they might be partiallyreacted during thermal processing to form a different species that couldalso be active in the catalytic reactions. An example is the reactionproduct derived from porphyrins or other organic compounds.

Molecular metal precursors with decomposition temperatures below about300° C. allow the formation of catalyst particles coated with an ion-and electron-conductive coating on a substrate such as a PEM layer or asheet of carbon paper. This enables the liquid medium, a molecular metalprecursor and a conducting polymer to be processed at low temperaturesto form the desired electrode structure. In one embodiment, theconversion temperature is not greater than about 250° C., such as notgreater than about 200° C., more preferably is not greater than about150° C. and even more preferably is not greater than about 100° C. Theconversion temperature is the temperature at which the metal speciescontained in the molecular metal precursor compound is substantially (atleast 95 percent) converted to the pure metal.

A very significant feature of the present invention is the notion thatthe presence of an ion- and electron-conductive polymer affords us anexceptionally high degree of freedom in processing fuel cell electrodes,catalyst-coated membranes, and membrane-electrode assemblies withouthaving to worry about such issues as disrupting the electron-conductingpath or burying the carbon-supported catalyst particles deep into thePEM layer (which is otherwise not electron-conductive). We are free todispense the suspension to and form an electrode on either a primarysurface of a carbon paper sheet or a PEM film. The resulting coatingmaterial, being both ion- and electron-conductive, provides a bridge toestablish two networks of charge transport. This feature also allows usto laminate PEM, electrode, and diffuser layers together to form an MEAwith a wide processing window (e.g., the lamination pressure can behigher without inducing the detrimental effect of incapacitating asignificant proportion of catalyst particles by, for instance, buryingthem too deep into a PEM layer). The features of simple catalystsuspension compositions and ease of producing electrodes also enablesthe mass-production of MEAs on a continuous basis using a highlyadvantageous roll-to-roll process, explained as follows:

Referring to FIG. 8( a), as a preferred embodiment, the invented processmay include feeding a solid electrolyte membrane 34 intermittently orcontinuously from a feed roller 32. Two liquid dispensers 36, 38 areemployed to deliver a suspension from each side of membrane 34 onto itstwo primary surfaces (top and bottom surfaces shown in this figure). Byremoving the liquid medium from the suspension, one obtains catalyticelectrodes 40, 42 that are connected to the two respective primarysurfaces of the membrane to form a three-layer catalyst-coated membrane(CCM). At the same time, gas diffuser layers 46, 48 (continuous sheetsof carbon paper or cloth) are fed from two sets of rollers, 44 a, 44 band 44 c, 44 d, to sandwich the CCM layer to form a membrane-electrodeassembly 50 a or 50 b, which is being pulled or supported by a set ofrollers 49 a, 49 b. A cutting device may be provided to slice the MEA 50b into individual MEA pieces for use in a fuel cell system.

Alternatively, referring to FIG. 8( b), as another preferred embodiment,the invented process may include feeding a solid electrolyte membrane 34intermittently or continuously from a feed roller 32. Two liquiddispensers 36, 38 are employed to deliver a suspension onto a primarysurface of a gas diffuser layer, 46 or 48. By removing the liquid mediumfrom the suspension, one obtains catalytic electrodes 40, 42 that areconnected to the two respective primary surfaces of the diffuser layers46, 48. At the same time, catalytic electrode-coated gas diffuser layers46, 48 are fed from two sets of rollers, 44 a, 44 b and 44 c, 44 d, tosandwich the membrane layer 34 to form a membrane-electrode assembly 50a or 50 b, which is being pulled or supported by a set of rollers 49 a,49 b. A cutting device may be provided to slice the MEA 50 b intoindividual MEA pieces for use in a fuel cell system.

Another alternative arrangement, schematically shown in FIG. 8( c),entails a roll-to-roll process that begins with feeding a solidelectrolyte membrane 34 intermittently or continuously from a feedroller 32. Two liquid dispensers 36, 38 are employed to deliver asuspension from each side of membrane 34 onto its two primary surfaces(top and bottom surfaces shown in this figure). By removing the liquidmedium from the suspension, one obtains catalytic electrodes 40, 42 thatare connected to the two respective primary surfaces of the membrane toform a three-layer catalyst-coated membrane 52. This CCM may be woundaround a take-up roller 54 for later uses. Such a process also allowsfor mass production of CCMs which are commonly regarded as the mostdifficult fuel cell components to produce with consistent quality. Thepresently invented electro-catalyst composition ensures that twointertwine networks of charge transport for electrons and ions (e.g.,protons) are always preserved, relatively independent of the actualprocessing conditions.

Hence, as one preferred embodiment, the presently invented fuel cellelectrode-producing process comprises (a) preparing a first suspensionof first catalyst particles dispersed in a first liquid mediumcontaining a first polymer dissolved or dispersed therein; (b)dispensing the first suspension onto a primary surface of a substrateselected from an electronically conductive catalyst-backing layer (gasdiffuser plate) or a solid electrolyte membrane; (c) removing the liquidmedium to form the electrode that is connected to or integral with thesubstrate, wherein the polymer is both ion-conductive andelectron-conductive and the polymer forms a coating in physical contactwith the catalyst particles or coated on the catalyst particles; (d)dispensing a second suspension to a second primary surface of thesubstrate (or to a primary surface of a second substrate such as asecond carbon paper layer), wherein the second suspension comprisessecond catalyst particles dispersed in a second liquid medium containinga second polymer dissolved or dispersed therein; and (e) removing thesecond liquid medium to form an electrode connected to the secondprimary surface of the substrate (or connected to a primary surface ofthe second substrate), wherein the second polymer is both ion-conductiveand electron-conductive with an electronic conductivity no less than10⁻⁴ S/cm and ionic conductivity no less than 10⁻⁵ S/cm and the polymerforms a coating in physical contact with the second catalyst particlesor coated on the second catalyst particles.

If the substrate is a solid electrolyte membrane, the process isessentially what is described in FIG. 8( a). If the substrates are twoseparate gas diffuser layers, the process is essentially what isdescribed in FIG. 8( b). In each process, the catalytic electrode layers40, 42 can be obtained from (a) a suspension containing catalystparticles dispersed in a liquid medium or (b) a suspension containing amolecular metal precursor dissolved or dispersed in a liquid medium. Inthe latter case, a heating, energy, and/or radiation treatment may beutilized to induce a chemical reaction or physical transition forconverting the precursor to nano-scaled catalyst particles, unsupportedor supported on a conducting particle phase.

In a particularly preferred embodiment, the process may involveincluding a pore-forming means to produce pores in the resultingelectrode. Pore-forming means are well known in the art. For instance,physical or chemical blowing or foaming agents commonly used in theproduction of foamed plastics can be incorporated in the suspension.Alternatively, aero gel forming techniques may be used to produce a highlevel of porosity in the resulting electrode wherein a large number ofinterconnected pores are formed with pore walls being sub-micron ornanometer in size and, hence, the catalyst particles are readilyaccessible by the fuel (e.g., hydrogen gas) and oxidant (oxygen gas)that diffuse through these pores. These pore walls are both ion- andelectron-conductive.

A suspension can be prepared to contain only an ion- andproton-conductive polymer (or a mixture of two or three polymers)dissolved or dispersed in a solvent. Such a catalyst-free suspension isalso a useful material that can be coated to a primary surface of acarbon paper or a primary surface of a solid PEM layer. This is followedby depositing a thin film of the presently invented coated catalystparticles (composite electro-catalyst composition) from a suspensiononto either the carbon paper or the PEM layer. Such a catalyst-freecoating serves to ensure that the coated catalysts will have a completeelectronic connection with the carbon paper and complete ionicconnection with the PEM layer. The resulting electrode is characterizedin that the carbon black along with the supported Pt nano-particles arenot surrounded by the electronically non-conductive PEM polymer afterlamination to form a membrane-electrode assembly.

Therefore, another preferred embodiment of the present invention is aprocess of producing a fuel cell electrode on a substrate selected froma gas diffuser layer (e.g., carbon paper or cloth) or a solidelectrolyte membrane. The process comprises (a) preparing a firstsuspension or solution of a first liquid medium containing a first ion-and electron-conductive polymer dissolved or dispersed therein; (b)dispensing this first suspension or solution onto the substrate andremoving the first liquid to form a layer of first conductive polymeradhered to the substrate; and (c) depositing a catalyst composition ontothe first conductive polymer with the catalyst composition being bondedto, mixed with or integral with the first conductive polymer to form theelectrode. This electrode is characterized in that it comprises catalystparticles coated with or in physical contact with a conductive phasecomprising the first conductive polymer and that this conductive phasehas an electronic conductivity no less than 10⁻⁴ S/cm and ionicconductivity no less than 10⁻⁵ S/cm.

This step of depositing a catalyst composition may comprise (i)dispensing a second suspension of a second liquid medium with catalystparticles dispersed therein and a second ion- and electron-conductivepolymer dissolved or dispersed therein and (ii) removing the secondliquid to form the catalyst composition wherein the second conductivepolymer has an electronic conductivity no less than 10⁻⁴ S/cm and ionicconductivity no less than 10⁻⁵ S/cm. This second conductive polymer maybe the same material as the first conductive polymer. Alternatively,this second conductive polymer may be mixed with the first conductivepolymer during the deposition step to form the cited conductive phase.

Further alternatively, this step of depositing a catalyst compositionmay comprise (i) dispensing a second suspension of a second liquidmedium with a molecular metal precursor dispersed or dissolved thereinand a second ion- and electron-conductive polymer dissolved or dispersedtherein and (ii) converting the precursor to catalyst particles andremoving the second liquid to form the catalyst composition wherein thesecond conductive polymer has an electronic conductivity no less than10⁻⁴ S/cm and ionic conductivity no less than 10⁻⁵ S/cm. This secondconductive polymer may be the same material as the first conductivepolymer. Alternatively, this second conductive polymer may be mixed withthe first conductive polymer during the deposition step to form thecited conductive phase.

It may be noted that a roll-to-roll process has been suggested in theprior art for producing a catalyst-coated membrane or a membraneelectrode assembly; e.g., as described in Bonsel, et al. (U.S. Pat. No.6,197,147, Mar. 6, 2001) and Starz, et al. (U.S. Pat. No. 6,500,217,Dec. 31, 2002). However, these prior art processes did not make use of acatalyst composition capable of producing bi-networks of chargetransport paths and, hence, the produced CCMs or MEAs still had lowcatalyst utilization efficiency.

EXAMPLE 1 Preparation of poly(alkyl thiophene) as an Electron-ConductiveComponent

Water-soluble conductive polymers having a thiophene ring (X=sulfur) andalkyl groups containing 4, 6, 8, and 10 carbon atoms (m=4, 6, 8, or 10)in Formula III were prepared, according to a method adapted fromAldissi, et al. (U.S. Pat. No. 4,880,508, Nov. 14, 1989). The surfactantmolecules of these polymers were sulfonate groups with sodium, hydrogen,or potassium. Conductivity of polymers of this invention in a self-dopedstate was from about 10⁻³ to about 10⁻² S/cm. When negative ions from asupporting electrolyte used during synthesis were allowed to remain inthe polymer, conductivities up to about 50 S/cm were observed.Conductivities of polymers without negative ions from a supportingelectrolyte which were doped with vaporous sulfuric acid were about 10²S/cm.

A doped poly(alkyl thiophene) (PAT) with Y=SO₃H and A=H in Formula IIIthat exhibited an electron conductivity of 12.5 S/cm was dissolved inwater. A sulfonated poly(ether ether ketone)(PEEK)-based material calledpoly(phthalazinon ether sulfone ketone) (PPESK) was purchased fromPolymer New Material Co., Ltd., Dalian, China. With a degree ofsulfonation of approximately 93%, this polymer was soluble in an aqueoushydrogen peroxide (H₂O₂) solution. A water solution of 3 wt. %poly(alkyl thiophene) and an aqueous H₂O₂ solution of 3 wt. % sulfonatedPPESK was mixed at several PPESK-to-PAK ratios and stirred at 70° C. toobtain several polymer blend solution samples.

Samples of poly(alkyl thiophene)-PPESK mixtures in a thin film form wereobtained by casting the aforementioned solutions onto a glass plate,allowing water to evaporate. The proton and electron conductivity valuesof the resulting solid samples were then measured at room temperature.The results were shown in FIG. 5, which indicates that good electron andproton conductivities can be obtained within the range of 30-75% PPESK.

EXAMPLE 2 Inks (Suspensions) Containing poly(alkyl thiophene), PPESK,Carbon Black-Supported Pt or Pt/Ru

Carbon black-supported Pt and Pt/Ru catalyst particles were separatelyadded and dispersed in two aqueous polymer blend solutions prepared inExample 1. The PPESK-to-PAK ratio selected in both solutions was 1:1.The viscosity of the resulting solutions (more properly referred to assuspensions or dispersions) was adjusted to vary between a toothpaste-like thick fluid and a highly dilute “ink”, depending upon theamount of water used. These suspensions can be applied to a primarysurface of a carbon paper or that of a PEM layer (e.g. Nafion orsulfonated PEEK sheet) via spraying, printing (inkjet printing or screenprinting), brushing, or any other coating means.

A suspension comprising carbon black-supported Pt particles dispersed inan aqueous solution of PPESK and PAK was brushed onto the two primarysurfaces of a Nafion sheet with the resulting catalyst-coated membrane(CCM) being laminated between two carbon paper sheets to form a membraneelectrode assembly (MEA). In this case, the electrode was characterizedin that the carbon black along with the supported Pt nano-particles werecoated by or embedded in an ion- and electron-conductive polymer blend.A similar MEA was made that contained conventional Nafion-coatedcatalyst particles, wherein Nafion is only ion-conductive, but notelectron-conductive. The two MEAs were subjected to single-cellpolarization testing with the voltage-current density curves shown inFIG. 6. It is clear that coating the catalyst particles with anelectron- and ion-conductive polymer mixture significantly increases thevoltage output of a fuel cell compared with that of a conventional fuelcell with Nafion-coated catalysts. This implies a more catalystutilization efficiency and less power loss (lesser amount of heatgenerated).

EXAMPLE 3 Sulfonated polyaniline (S-PANi)

The chemical synthesis of the S-PANi polymers was accomplished byreacting polyaniline with concentrated sulfuric acid. The procedure wassimilar to that used by Epstein, et al. (U.S. Pat. No. 5,109,070, Apr.28, 1992). The resulting S-PANi can be represented by Formula I with R₁,R₂, R₃, and R₄ group being H, SO₃ ⁻ or SO₃H with the latter two beingvaried between 30% and 75% (degree of sulfonation between 30% and 75%).The proton conductivity of these SO₃ ⁻- or SO₃H-based S-PANI)compositions was in the range of 3×10⁻³ S/cm to 4×10⁻² S/cm and theirelectron conductivity of 0.1 S/cm to 0.5 S/cm when the degree ofsulfonation was from approximately 30% to 75% (with y beingapproximately 0.4-0.6).

A sample with the degree of sulfonation of about 65% was dissolved in0.1 M NH₄OH up to approximately 20 mg/ml. A small amount ofcarbon-supported Pt was added to the S-PANi solution to obtain asuspension that contained approximately 5% by volume of solid particles.The suspension was sprayed onto the two primary surfaces of a Nafionsheet with the resulting catalyst-coated membrane (CCM) being laminatedbetween two carbon paper sheets to form a membrane electrode assembly(MEA). Prior to this lamination step, one surface of the carbon paper,the one facing the catalyst, was pre-coated with a thin layer of S-PANivia spraying of the S-PANi solution onto the paper surface and allowingthe solvent to evaporate under a chemical fume hood. The resultingelectrode was characterized in that the carbon black along with thesupported Pt nano-particles were coated by or embedded in an ion- andelectron-conductive polymer. The electrode was also porous, providingchannels for fuel or oxidant transport. A similar MEA was made thatcontained conventional Nafion-coated catalyst particles, wherein Nafionis only ion-conductive, but not electron-conductive. The two MEAs weresubjected to single-cell polarization testing with the voltage-currentdensity curves shown in FIG. 7. These results demonstrate that coatingthe catalyst particles with an electron- and ion-conductive polymersignificantly increases the voltage output of a fuel cell compared withthat of a conventional fuel cell with Nafion-coated catalysts.

EXAMPLE 4 Bi-Cyclic Conducting Polymers

The preparation of conductive polymers represented by Formula II havingH for both R₁ and R₂, S for X, and H⁺ for M was accomplished byfollowing a procedure suggested by Saida, et al. (U.S. Pat. No.5,648,453, Jul. 15, 1997). These polymers exhibit electronicconductivity in the range of 5×10⁻² S/cm to 1.4 S/cm and protonconductivity of 5×10⁻⁴ S/cm 1.5×10⁻² S/cm.

Six polymer blends were prepared from such a bi-cyclic polymer (electronconductivity σ_(e)=1.1 S/cm and proton conductivity σ_(p)=3×10⁻³ S/cm)and approximately 50% by wt. of the following proton-conductivepolymers: poly(perfluoro sulfonic acid) (PPSA), sulfonated PEEK(S-PEEK), sulfonated polystyrene (S-PS), sulfonated PPESK, sulfonatedpolyimide (S-PI), and sulfonated polyaniline (S-PANi). Theconductivities of the resulting polymer blends are σ_(e)=0.22 S/cm andσ_(p)=2×10⁻² S/cm for (bi-cyclic+PPSA), σ_(e)=0.2 S/cm and σ_(p)=7×10⁻³S/cm for (bi-cyclic+S-PEEK), σ_(e)=0.23 S/cm and σ_(p)=5.5×10⁻³ S/cm for(bi-cyclic+S-PS), σ_(e)=0.19 S/cm and σ_(p)=6×10⁻³ S/cm for(bi-cyclic+S-PPESK), σ_(e)=0.21 S/cm and σ_(p)=7.5×10⁻³ S/cm for(bi-cyclic+S-PI), and σ_(e)=0.75 S/cm and σ_(p)=3×10⁻³ S/cm for(bi-cyclic+S-PANi), These conductivity values are all within theacceptable ranges for these polymer blends to be a good coating materialfor the catalyst particles in a fuel cell electrode.

EXAMPLE 5 Suspension Comprising a Molecular Metal Precursor

Preferred molecular precursors include chloroplatinic acid(H₂PtCl₆—H₂O), tetraamineplatinum (II) nitrate (Pt(NH₃)₄(NO₃)₂,tetraamineplatinum (II) hydroxide (Pt(NH₃)₄(OH)₂), tetraamineplatinum(II) bis(bicarbonate) (Pt(NH₃)₄(HCO₃)₂), platinum nitrate (Pt(NO₃)₂),hexa-hydroxyplatinic acid (H₂Pt(OH)₆), platinum (II) 2,4-pentanedionate(Pt(acac)₂), and platinum (II) 1,1,1,5,5,5-hexafluoro 2,4-pentanedionate(Pt(hfac)₂). Other platinum precursors include Pt-nitrates, Pt-aminenitrates, Pt-hydroxides, Pt-carboxylates, Na₂PtCl₄, and the like.Typically, the Pt precursor was dissolved in either water ororganic-based solvent up to 30% by weight concentration.

Using water solution as an example, chloroplatinic acid (H₂PtCl₆—H₂O)was dissolved in water for up to 15% by weight. On a separate basis, anaqueous ethanol solution of 3% by weight sulfonated polyaniline wasprepared. The two solution was mixed together to form a suspension whichwas stirred for 30 minutes. This suspension was divided up into twobeakers with one of them being added with carbon black particles toserve as a catalyst support. A desired quantity of each suspension wascast onto a primary surface of each of two sheets of carbon paper toproduce an electrode-coated carbon paper (or carbon paper-backedelectrode). A Nafion film was then sandwiched between the two carbonpaper-supported electrodes to form a membrane electrode assembly. Amolecular precursor conversion temperature of 250° C. was used toproduce the catalyst particles. Actually, both chloroplatinic acid(H₂PtCl₆—H₂O) and hexa-hydroxyplatinic acid (H₂Pt(OH)₆) can bedecomposed at a temperature lower than 150° C. while tetraamineplatinum(II) nitrate (Pt(NH₃)₄(NO₃)₂, tetraamineplatinum (II) hydroxide(Pt(NH₃)₄(OH)₂), tetraamineplatinum (II) bis(bicarbonate)(Pt(NH₃)₄(HCO₃)₂), and platinum nitrate (Pt(NO₃)₂) can be decomposed ata temperature lower than 300° C. It may be note that polyaniline-basedpolymers are stable up to 350° C. and, hence, the precursor conversionstep would not adversely affect the structure of these conductivepolymers. In some cases, the removal of the reaction product gases(e.g., NH₃) naturally leave behind pores in the electrode, which is adesirable feature since pores facilitate diffusion of fuel (hydrogen)and oxidant gases (oxygen).

EXAMPLE 6 The Preparation of Particles Including an Alloy of Palladiumand Nickel

Palladium and nickel wires were subjected to a twin-wire arc-based nanoparticle production process. A high pulse current of 240 amps was usedto create the arc. The Pd and Ni atoms in the vaporous phase collidedand condensed to form nano particles of approximately 2-5 nm in size.

In addition, for the purpose of comparison, an aqueous solution wasprepared including nickel and palladium as dissolved nitrates. The totalof the metals in the mixture is 5 weight percent. The nickel andpalladium were proportioned at 30/70 Pd/Ni by weight. The solution wassonicated for 30 minutes to ensure uniformity. A single transducerultrasonic generator was then used to produce an aerosol, which was sentto a furnace at a temperature of 900° C. where particles were produced.The aerosol carrier gas comprises 95 percent nitrogen by volume and 5percent hydrogen by volume. The resulting particles have a size range of4 nm to 10 nm.

Palladium and its alloys were particularly useful anode catalysts fordirect formic acid fuel cell.

EXAMPLE 7 Production of a Membrane Electrode Assembly

The reaction between 1,3-divinyl-1,1,3,3-tetramethyldisiloxane andhexachloroplatinic acid led to Pt-based nano particles. The liquidreaction product contain approximately 18 wt.-% of platinum hereinreferred to as Pt-VTS. Pt-VTS can be decomposed at a relatively lowtemperature, e.g. by drying at a temperature of 110° C. Extremely finelydivided, metallic platinum remained while the silicon content of thevinyl-substituted siloxanes could no longer be detected in the finishedcatalyst layers. Other suitable complex compounds of the precious metalsiridium, ruthenium and palladium for use in practicing the presentinvention are dodecacarbonyltetrairidium (Ir₄(CO)₁₂),(η⁶-benzene)(ρ⁴-cyclohexadiene)ruthenium(0) ((η⁶-C₆H₆)Ru(η⁴-1,3-C₆H₈))and bis(dibenzylideneacetone)-palladium(0).

The reaction product Pt-VTS was prepared following the proceduresuggested by U.S. Pat. No. 3,775,452. For instance, 20 parts by weightsodium carbonate were added to a mixture of 10 parts by weightH₂PtCl₆.8H₂O, 20 parts by weight1,3-divinyl-1,1,3,3-tetramethyldisiloxane and 50 parts by weightethanol. The mixture was boiled for 15 minutes and then a solution ofsolfonated polyaniline in ethanol-water and Vulcan XC72 carbon blackwere added to the boiling mixture. The resulting suspension wassubjected to sonification for 30 minutes and then dispensed anddeposited onto two primary surfaces of a Nafion-115 film to produce acatalyst-coated membrane, which was then sandwiched between two sheetsof carbon paper to produce a membrane-electrode assembly.

1. A process for producing a fuel cell electrode, said processcomprising: (a) preparing a first suspension or solution comprising thesequential steps a first liquid medium, a first molecular metalprecursor with no particulate support material, and a first polymerdissolved or dispersed in said first liquid medium; (b) dispensing saidfirst suspension or solution onto a first primary surface of a substrateselected from a first electronically conductive catalyst-backing layeror a solid electrolyte membrane; and (c) converting said first molecularmetal precursor to catalyst particles and removing said first liquidmedium to form a first electrode connected to or integral with saidsubstrate, wherein said first polymer is both ion-conductive andelectron-conductive with an electronic conductivity no less than 10⁻⁴S/cm and ionic conductivity no less than 10⁻⁵ S/cm and said polymerforms a coating in physical contact with said catalyst particles orcoated on said catalyst particles.
 2. The process of claim 1 whereinsaid step of converting comprises a heat-, ultraviolet, and/orradiation-induced chemical reaction.
 3. The process of claim 1 whereinsaid catalyst particles comprise a catalytically active materialselected from the group consisting of Pt, Ag, Pd, Ru, Os, Ni, Rh, Ir,Co, Cr, Mo, W, V, Nb, Al, Ta, Ti, Zr, Hf, Zn, Fe, Cu, Ga, In, Si, Ge,Sn, Y, La, lanthanide metals, and mixtures, alloys, and oxides of thesemetals.
 4. The process of claim 1 further comprising pore-forming meansand said electrodes comprise pores.
 5. The process of claim 4 whereinsaid pore-forming means comprises using and activating a blowing orfoaming agent or producing an aerogel.
 6. The process of claim 1 whereinsaid polymer comprises a mixture of an electronically conductive polymerand a proton-conducting polymer selected from the group consisting ofpoly(perfluoro sulfonic acid), sulfonated polytetrafluoroethylene,sulfonated perfluoroalkoxy derivatives of polytetrafluoroethylene,sulfonated polysulfone, sulfonated poly(ether ketone), sulfonatedpoly(ether sulfone ketone), sulfonated poly(ether ether ketone),sulfonated polyimide, sulfonated styrene-butadiene copolymers,sulfonated polychlorotrifluoroethylene, sulfonatedperfluoroethylene-propylene copolymer, sulfonatedethylene-chlorotrifluoroethylene copolymer, sulfonated polystyrene,sulfonated polyvinylidenefluoride, sulfonated copolymers ofpolyvinylidenefluoride with hexafluoropropene and tetrafluoroethylene,sulfonated copolymers of ethylene and tetrafluoroethylene,polybenzimidazole, their chemical derivatives, copolymers, blends, andcombinations thereof.
 7. The process of claim 1 wherein said polymercomprises an electronically conducting polymer.
 8. The process of claim1, wherein said polymer comprises an electronically conducting polymerselected from the group consisting of sulfonated polyaniline, sulfonatedpolypyrrole, sulfonated poly thiophene, sulfonated bi-cyclic polymers,their derivatives, and combinations thereof.
 9. The process of claim 1wherein said first molecular metal precursor comprises ametal-containing molecular compound selected from the group consistingof organo-metallics with at least a carbon-metal bond; metal organicscontaining at least an organic ligand with a metal-to-non-metal bond;and inorganic compounds selected from metal nitrates, metal halides,carboxylates, alkoxides, ammonium salts of platinates, complex compoundsof platinum, iridium, ruthenium and palladium, and metal salts ofplatinum, iridium, ruthenium and palladium; and combinations thereof.10. The process of claim 1 wherein said catalyst particles comprise acatalytically active material selected from the group consisting of Pt,Ag, Pd, Ru, Os, Ni, Rh, Ir, Co, Cr, Mo, W, V, Nb, Al, Ta, Ti, Zr, Hf,Zn, Fe, Cu, Ga, In, Si, Ge, Sn, Y, La, lanthanide metals, and mixtures,alloys, and oxides of these metals.
 11. The process of claim 1 whereinsaid substrate is a solid electrolyte membrane intermittently orcontinuously supplied from a feeder roller and said process furthercomprises: (d) dispensing a second suspension to a second primarysurface of said substrate, wherein said second suspension comprises asecond molecular metal precursor dispersed or dissolved in a secondliquid medium containing a second polymer dissolved or dispersedtherein; and (e) converting said second molecular precursor to secondcatalyst particles and removing said second liquid medium to form asecond electrode connected to the second primary surface of saidsubstrate, wherein said second polymer is both ion-conductive andelectron-conductive with an electronic conductivity no less than 10⁻⁴S/cm and ionic conductivity no less than 10⁻⁵ S/cm and said polymerforms a coating in physical contact with said second catalyst particlesor coated on said second catalyst particles; wherein said firstelectrode, said solid electrolyte membrane, and said second electrodeform a catalyst-coated membrane.
 12. The process of claim 11 furthercomprising a step of bringing a sheet of electrically conductive fueldiffuser plate onto one surface of said catalyst-coated membrane andbringing a sheet of oxidant diffuser plate onto another surface of saidcatalyst-coated membrane to form a membrane-electrode assembly.
 13. Theprocess of claim 1 wherein said substrate is a first gas diffuser sheetintermittently or continuously supplied from a first feeder roller andsaid process further comprises: (d) feeding, intermittently orcontinuously, a second gas diffuser sheet from a second feeder roller;(e) dispensing a second suspension to a primary surface of said seconddiffuser sheet, wherein said second suspension comprises a secondmolecular metal precursor dissolved or dispersed in a second liquidmedium containing a second polymer dissolved or dispersed therein; (f)converting said second molecular metal precursor to second catalystparticles and removing said second liquid medium to form an electrodeconnected to said primary surface of said second diffuser sheet, whereinsaid second polymer is both ion-conductive and electron-conductive withan electronic conductivity no less than 10 ⁻⁴ S/cm and ionicconductivity no less than 10⁻⁵ S/cm and said polymer forms a coating inphysical contact with said second catalyst particles or coated on saidsecond catalyst particles; and (g) feeding a sheet of solid electrolytemembrane between the electrode of said first diffuser sheet and theelectrode of said second diffuser sheet to form a membrane-electrodeassembly.
 14. The process of claim 4 wherein said pore-forming meanscomprises forming aero gels with pore walls comprising said ion- andelectron-conducting polymer and said catalyst particles in said walls.